Engine Management

ABSTRACT

An in-cylinder pressure sensor obtains a high resolution pressure curve for each cylinder cycle allowing the various data to be derived for improved monitoring and control of operation of the engine. A more accurate measure of work done by the engine is obtained allowing more accurate estimation of the vehicle torque and hence real torque control. In addition, engine losses can be more accurately calculated and the estimates corrected yet further by obtaining an accurate top dead centre position for the engine cylinders.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of application Ser. No. 10/536,619,filed Aug. 25, 2006, the entire disclosure of which is herebyincorporated by reference.

BACKGROUND OF THE INVENTION

The invention relates to a system and method providing improved enginemanagement and in particular using real time cylinder pressure data. Theaspects discussed herein are an extension of the concepts disclosed inInternational patent application no. PCT/GB02/02385 entitled “ImprovedEngine Management” commonly assigned herewith and incorporated herein byreference.

Known engine management systems (EMS) monitor and control the running ofan engine in order to meet certain pre-set or design criteria. Typicallythese are good drivability coupled with high fuel efficiency and lowemissions. One such known system is shown schematically in FIG. 1. Aninternal combustion engine 10 is controlled by an engine control unit 12which receives sensor signals from a sensor group designated generally14 and issues control signals to an actuator group designated generally16. The engine control unit 12 also receives external inputs fromexternal input block 18 as discussed in more detail below.

Based on the engine performance data derived from the sensor input fromthe sensor block 14 and any external input from the external input block18 the engine control unit (ECU) optimizes engine performance by varyingthe relevant performance input variable within the specified criteria.

Typically the sensor block 14 may include sensors including mass airflowsensors, inlet temperature sensors. knock detection sensors, cam sensor.air/fuel ratio (AFR) or lambda (λ) sensors, and engine speed sensors.The external input block 18 typically includes throttle or acceleratorsensors, ambient pressure sensors and engine coolant temperaturesensors. In a spark-ignition engine the actuator block 16 typicallycomprises a fuel injector control and spark plug operation control. In acompression ignition engine the actuator block typically comprises afuel injector.

As a result, for example in spark ignition engines, under variable loadconditions induced by the throttle under driver control, the sensors andactuators enable effective control of the amount of fuel entering thecombustion chamber in order to achieve stoichiometric AFR, and of thetiming of combustion itself.

Known engine management systems suffer from various problems. EMStechnology remains restricted to parameter based systems. These systemsincorporate various look-up tables which provide output values based oncontrol parameters such as set-points, boundaries, control gains, anddynamic compensation factors, over a range of ambient and engineoperating conditions. For example in spark ignition engines spark timingis conventionally mapped against engine speed and engine load andrequires compensation for cold starting. In compression ignition enginesfuel injection timing is mapped in a similar manner. As well asintroducing a high data storage demand, therefore, known systems requiresignificant initial calibration. This calibration is typically carriedout on a test bed where an engine is driven through the full range ofconditions mapped into the look-up tables. As a result the systems donot compensate for factors such as variations between engine builds letalone individual cylinders, and in-service wear. Accordingly the look-uptables may be inaccurate ab initio for an individual engine, and willbecome less accurate still with time.

In one aspect known systems control vehicle performance based on aconsideration of engine conditions together with mappings. Thesemappings are derived during vehicle calibration and can include physicalparameters related to engine geometry. Generally much of the engineperformance data is very indirect and is based on multiple inferencesfrom sensors together with the mapped or modeled data which can giverise to inaccuracies arising from the inferences made or fromdifferences between vehicles based on production tolerances or indeeddifferences between conditions in individual cylinders within an engine.The latter is mainly due to differences in air and inert gas paths,temperatures of the cylinder walls and production tolerances ofvalvetrain and piston/crankshaft geometry. Furthermore such approachesdo not compensate for changes in performance arising from in-servicewear.

One known system comprises adjusting performance input variables to theengine to control engine torque to a target. A problem with this is thatthe engine torque is in fact inferred from easily measurable variablessuch that airflow in a gasoline engine or fuel flow in a diesel engine.Accordingly the value for torque that is derived is indirect andinaccurate, suffering from the disadvantages set out above. Althoughtorque sensors are known, these are costly and are not robust. Knownsystems also derive a measure of engine frictional losses represented bythe friction mean effective pressure (FMEP). However in known systemsthese values are currently mapped or modeled at the engine manufacturestage and hence suffer from the problems set out above.

The invention is set out in the claims.

BRIEF DESCRIPTION OF THE FIGURES

Embodiments of the invention will now be described by way of examplewith reference to the drawings, of which:

FIG. 1 is a block diagram representing a prior art EMS;

FIG. 2 is a schematic diagram representing an EMS according to thepresent invention;

FIG. 3 is a schematic view of a single cylinder in cross sectionaccording to the present invention;

FIG. 4 is a trace of pressure against crank angle for a cylinder cycleof a four stroke engine;

FIG. 5 is a trace showing IMEP for a cylinder cycle;

FIG. 6 is a plot of pressure against crank angle θ showing pressurevariation of a motoring pressure curve to demonstrate top dead centre;

FIG. 7 is a block diagram showing control modules in an engine accordingto the present invention;

FIG. 8 is a block diagram showing the components of an EMS according tothe present invention;

FIG. 9 is a block diagram showing individual cylinder control in an EMSaccording to the present invention; and

FIG. 10 shows the pressure cycle for the selected cylinder in asix-cylinder engine.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following discussion of an embodiment of the invention relates toits implementation in relation to a four stroke combustion ignitionengine comprising a diesel engine. However it will be appreciated thatthe invention can be applied equally to other stroke cycles and types ofinternal combustion engines including spark-ignition engines, withappropriate changes to the model parameters. Those changes will beapparent to the skilled person and only the best mode presentlycontemplated is described in detail below. Like reference numerals referto like parts throughout the description.

FIG. 2 is a schematic view showing the relevant parts of an enginemanagement system according to the present invention in conjunction witha six cylinder engine. An engine control unit is designated generally 20and controls an engine designated generally 22. The engine includes sixcylinders designated generally 24. Each cylinder includes a pressuresensor 26 which connects to the ECU via a line 28. In addition the ECUprovides electronic control to each of the cylinder injectors (notshown). The ECU 20 can also receive additional controls and actuatorinputs 32 as discussed in more detail below. The engine managementsystem monitors the pressure in each cylinder through each completeengine cycle. namely 720⁰ rotation of the crankshaft in a four-strokeengine. Based on this data the injection timing for each. cylinder 24 isvaried by varying the timing of each injector via control lines 30.

In FIG. 3 there is shown schematically a more detailed view of a singlecylinder 24 of the engine. The in-cylinder pressure sensor 26 comprisesa piezoresistive combustion pressure sensor with a chip made of siliconon insulator (SOI) available from Kistler Instrumente AG, Winterthur,Switzerland as transducer Z17619, cable 4767 A2/5/10 and amplifierZ18150. It will be appreciated that any appropriate in-cylinder pressuresensor can be used, however. For example the sensor can be of the typedescribed in co-pending application number DE 100 34 390.2. The pressuresensor 26 takes continuous readings through the four strokes of thepiston 40. The readings are crank-synchronous and triggered by crankteeth 42 a of the crank 42, detected by a crank tooth sensor 44 whichsends an appropriate signal via line 46 to the ECD 20. In the preferredembodiment readings are taken every 2° of crankshaft rotation althoughany desired resolution can be adopted, the limiting factors beingprocessing power and crank angle sensing resolution. For each cylinderthe readings are taken across a cycle window of width 7200. As discussedin more detail below with reference to FIG. 16, the window is selectedto run from a point substantially before engine top dead centre (TDC)for each cylinder.

The data obtained from the in-cylinder sensor 26 is processed asdiscussed in more detail below and a high resolution plot of pressureversus crank angle (which can be simply converted to time if the enginespeed is known) is obtained for each cylinder and each cycle. From thisinformation, monitoring and control of engine performance is greatlyenhanced.

In overview, in the first aspect the invention makes use of thepossibility of deriving the work done by each cylinder piston in theengine from in-cylinder measurements of the cylinder pressure. Inparticular the indicated mean effective pressure (IMEP) is derived fromthe pressure information combined with the corresponding cylinder volumeat each cycle. The brake mean effective pressure (BMEP), which is ameasure of engine output torque, at any point from and including thecrankshaft to the transmission system, can then be derived from the IMEPand the losses represented by the FMEP which are calibrated or modeled.As a result mapped measurements are restricted to the FMEP calculationsrendering the determination of the output torque more accurate. This isthen used to adjust the performance input parameters to control theoutput torque to a target desired output torque providing torque basedcontrol.

In a second aspect an estimate or sensed value for the BMEP is obtainedand, using the measured value of IMEP the FMEP is derived, again moreaccurately because of the direct measurement of IMEP. In this case therelevant information which relates to losses in the vehicle can be usedfor on-board diagnostics (OBD) systems. The derivations of BMEP and FMEPin the respective aspects can be cross-correlated with their respectiveestimated values in the alternative aspect allowing the mappings ormodels to be refined based on real vehicle performance and accountingfor variations/deterioration with time.

Although the following discussion relates principally to IMEP, itapplies equally to equivalent measures of engine output such as torqueor power, and appropriate units and conversions should be inferred asappropriate. For example as regards engine shaft output, a measure ofthis can be expressed as the brake mean effective pressure BMEP asdiscussed in more detail below, engine output torque, engine outputpower and so forth. A measure of engine frictional losses may beexpressed as the FMEP, as friction torque or as friction power and ameasure of work done on the piston of a cylinder can be expressed as theIMEP, indicated torque or indicated power. In each case yet furtherexpressions may be used as appropriate.

In either case IMEP must be calculated which requires a correlation ofthe measured pressure in the cylinder with the corresponding cylindervolume at any time. The cylinder volume at any time is known from thecrank angle which is directly related to the piston position. Howeverbecause of mechanical tolerances and variations between engines andindividual cylinders, the relationship between volume and crank anglemay differ slightly between engines and individual cylinders, sufficientto affect the IMEP calculation. Accordingly the invention furtherextends to obtaining a more accurate measurement of piston top deadcentre (TDC) each cylinder and each cycle allowing a correspondinglymore accurate measurement of IMEP.

The pressure data derived is shown in FIG. 4 which shows the cylinderpressure variation against crank angle for one full cycle between −360°and +360°. As is well known the engine cycle is divided into fourregions, induction from −360° to −180°, compression from −180° to 0°(TDC), expansion from 0° to +180° and exhaust from +180° to 360°,defining a full 720° cycle. Theoretically, for instantaneous combustionoccurring over an infinitely small period of time the optimum point forcombustion is at 0° TDC, but in practice injection timing can vary byseveral degrees from TDC.

The pressure curve obtained is then processed to provide additionalengine performance data allowing enhanced control.

In the first aspect, the pressure curve is used to obtain a measure ofmean engine torque in the form of the BMEP at the engine output based onthe direct relationship between BMEP and torque. In particular it can beshown that for a four stroke engine:

$\frac{B\; M\; E\; {P \cdot V_{S} \cdot N}}{2} = {{\tau \cdot N \cdot 2}\pi}$

Where V_(S)=swept volume of all cylinders.

N=number of revolutions and τ=torque.

This can be simplified to

As a result it can be seen that tracking the BMEP allows tracking of thevehicle torque.

Now BMEP is given by the difference between the work done by the engineand the subsequent losses, i.e:

BMEP=IMEP−FMEP

where the FMEP represents the losses between the net work done by thegases in the cylinders and the point in the engine where BMEP isreferenced. These losses are due to crankshaft and piston friction,valvetrain losses, air conditioning, power steering, side mountedelectrical machine losses and so forth.

The FMEP can be derived in various manners. In one approach it can bemapped or modeled based on detected engine conditions with a map ormodel constructed during engine prototyping. Alternatively the FMEP canbe derived by monitoring deceleration (in conjunction with the vehicleroad information) during skip firing in an overrun or crankingconfiguration. Here as the cylinder is not being fired. the decelerationis caused because of the losses in the vehicle including decelerationowing to gravity when the vehicle is on a slope, aerodynamic losses andmechanical losses in the powertrain which in turn are made up of thelosses between the wheels and the point where BMEP is referenced(rolling resistance, transmission and differential losses and so forth),and FMEP. Appropriate sensors models or maps can be used to obtain thevalue of the relevant losses. At low speeds aerodynamic losses can beignored and the effect of gravity cancelled out if the road gradient isknown (by an inclination sensor, for example). As a result only themechanical losses need to be estimated to obtain FMEP. Furthermore, whenskip-firing individual cylinders, a comparison can be made of theirrespective FMEPs. This is useful for detecting failures such as pistonring deterioration.

Yet a further approach is to apply the “morse test” which is known tothe skilled reader as described in Introduction to Internal CombustionEngines, Richard Stone, Second Edition, Macmillan, 1992, pp 476-477 inwhich individual cylinders are sequentially skip fired and the RPM losssummed to obtain a measure of the FMEP.

The work done by the gases on the piston for each engine cycle can berepresented by the IMEP over the engine cycle as represented in FIG. 5which shows a plot of cylinder pressure, P against volume V over asingle four-stroke cycle. The area shown shaded is the gross IMEPrelating to the work done during the compression and expansion strokeswhile the area enclosed by the entirety of the plot is the net IMEPrelating to the work done over the whole cycle, including work done onthe gases by the piston during the induction and exhaust strokes. Thegross IMEP region is also shown on the pressure versus crank angle plotof FIG. 4.

Because the samples taken are sufficient to plot the Pressure/Volumecurve the IMEP for a single cylinder can be obtained empirically byapplying trapezoidal integration yielding, for the net IMEP:

${I\; M\; E\; P_{net}} = {{\frac{1}{V_{cs}}{\sum\limits_{l = 1}^{m - 1}{\frac{P_{l} + P_{i + 1}}{2}\left( {V_{i + 1} - V_{l}} \right)\mspace{31mu} m}}} = \frac{720}{\theta_{res}}}$

where V_(cs) is the swept volume of one cylinder. This net IMEP will bereferred to here onwards as ‘IMEP’.

Equation (4) is preferably calculated based on the raw pressure data asthe effects of noise are reduced because the IMEP is effectivelyobtained by integration. Similarly any pressure off-set correctionrequired for medium to long-term sensor drift, is irrelevant to the IMEPcalculation since it is a cycle integral of the area enclosed the PVdiagram of FIG. 7 and so it is independent of absolute pressure values.

Once the IMEP and FMEP is obtained then the BMEP can be similarlyobtained by the above equation. It will be noted that if FMEP isindirectly measured using a skip firing or similar technique then thiscan be correlated against the mapped or modeled FMEP to refine the mapor model appropriately.

As a result, real torque control is obtained where a more accurate modelof the engine torque is derived. The engine performance input variablescan then be adjusted to track BMEP to a target value demanded by thedriver or EMS. This can be done either to optimize vehicle torque or tomaintain it stable dependent on the driving mode required. Stability isparticularly attractive if the engine is switching between operatingmodes (for example in order to regenerate exhaust after treatmentsystems).

Because the model is based on a restricted set of assumptions it iscorrespondingly enhanced and hence compensates for variations betweenengines and cylinders. The real torque based control system henceprovides the possibility of improved idle speed control improvedtransmission control and improved torque based control during enginemode switching such as switching of air/fuel ratios betweenstoichiometric lean and rich mixtures switches between compressionignition modes such as homogeneous and stratified modes. variations incompression ratio switches between compression ignition and sparkignition cylinder de-activation and switches between two stroke and fourstroke operation. Yet further the invention provides improved torquecontrol for hybrid engines for example electric/fuel or bi-fuel hybrids.

In a second aspect a similar approach to that identified above isadopted but to obtain a measure of the losses in the vehicle in the formof the FMEP. FMEP can be obtained by rearranging equation (3) to obtain:

FMEP=IMEP−BMEP

As discussed above IMEP can be derived from direct in-cylinder pressuremeasurements during each cylinder cycle.

BMEP can be obtained in a known manner for example by estimation from avehicle model or from a torque sensor in conjunction where appropriatewith factors such as the vehicle weight and road inclination. In thatcase the estimation of FMEP is enhanced as it is based on reducedassumptions. The FMBP can be used to allow feedback to torque control orcan be used in conjunction with the first aspect to allow respectiverefinement of the BMEP and FMEP values as the values calculated for eachby respective equations (3) and (5) can be correlated against thederived values from the model or map.

In one embodiment estimation of FMEP is scheduled at predeterminedintervals, for example, a predetermined driven distance allowing vehiclelosses to be determined at various intervals and operation according tothe first aspect to continue the rest of the time.

As a result the second aspect allows fault or wear diagnosis to beperformed by monitoring vehicle losses in the form of FMEP and/or allowsenhancement of real torque based control.

It will be seen that both firsts and second aspects of the invention,i.e. calculation of the BMEP or FMEP rely on an accurate derivation ofthe engine IMEP. Referring to the equation set out above and FIG. 5,IMEP is obtained by the integration of PdV, requiring V_(i), thecylinder or volume at a given reading instant i to be known inconjunction with P_(i). The cylinder volume depends on the pistonposition which is known from the crank angle. In the preferredembodiment, however, TDC is measured from the pressure data itselfallowing the cylinder volume to be more accurately synchronized with thecylinder pressure.

Referring to FIG. 6, the specific TDC required is the mechanical TDC 50,that is, the point in time at which the cylinder volume is at a minimum.This differs from the thermodynamic TDC 52 at which the motored cylinderpressure is at a maximum simply because of the thermodynamics of thegas. In particular the thermodynamic TDC 52 will lag the mechanical TDC50 by a thermodynamic loss angle TLA 54. This lag can be mapped duringengine prototyping or modeled, as will be apparent to the skilledreader, from heat release analysis. The engine speed of course needs tobe taken into account as this will affect the offset, again as known tothe skilled reader. For the purposes of calculated IMEP the mechanicalIDC is required as this relates to the actual volume in the cylinder.

Accordingly to obtain TDC, the thermodynamic TDC is first obtained fromthe motoring curve 56. The motoring curve is the pressure curve thatwould be obtained if combustion did not take place in the cylinder,representing purely the varying pressure resulting from the compressionstroke in the cylinder.

The motoring curve 56 can be derived in various ways known to theskilled person. For example it can be calibrated or obtained by “skipfiring” in which at certain intervals fuel is not injected into thecylinder for one cycle (e.g. during cranking or overrun) and theresultant pressure curve obtained.

Once the motoring curve is derived, then to obtain the thermodynamic IDCthe maximum pressure P_(max) 58 is obtained. It will be seen that thevalue is easily derivable simply by selecting the maximum on the curveas shown in FIG. 6. The relevant point can be identified in anyappropriate way, for example by differentiating the curve andidentifying the crossover point between positive and negative gradient.Depending on the resolution of the measured data, the maximum can beinterpolated between adjacent data points, for example by usingpolynomial curve fitting techniques as will be well known to the skilledreader.

The mechanical TDC 50 can then be obtained by subtracting the TLA 54,corrected for engine speed, from the thermodynamic TDC. This can then“be used to correct the value of V in equation (4). For example thedifference between the measured mechanical mc and the assumed mechanicalTDC can be applied as a correction for each value of V_(i).

As a result a more accurate IMEP value is obtained.

It will be noted that the thermodynamic mc 52 can also be used directlyfor example for governing combustion events such as spark time orinjection timing control.

As a result the preferred approach compensates for mechanical tolerancesas well as in-service wear allowing improved IMEP estimation. TDC can bederived for each cycle or can be measured at predetermined intervals toensure that the true TDC and assumed TDC remain equivalent.

Any appropriate control mechanism and strategy can be adopted toimplement the various enhancements discussed above, as will be apparentto the skilled person. One appropriate system is discussed in overviewwith reference to FIG. 7 and includes a controller 100, one or moreactuators 102, cylinder 104, processor 106 and a module 108 supporting amodel or map correlating predetermined values. The measured pressurefrom the cylinder together with the corresponding crank angle θ_(a) arefed to the processor 106 which derives a pressure curve and/or pressurevalue and from those performance output variables such as temperature,heat release, AFR and so forth as discussed above. These parameters areoutput to a controller 100 together with other necessary sensor inputsfrom a sensor or sensors 110.

Where necessary the controller takes these inputs and feeds them to themodel or mapping module 108 in order to obtain the desired adjustedperformance input variables. The module 108 can be calibrated duringengine prototyping on the test-bed, for example, to provide mappingsbetween performance output values such as BMEP and desired performanceinput variables such as fuel injection timing and quantity.

The adjusted performance input variables are then fed to the relevantactuators 102 which control conditions in the cylinder 104. As a resulta feedback loop is provided in which the, measured pressure valueprovides a performance output value which is either controlled to tracka target performance output value, or which can be used as a check orcorrelation against values obtained from the module 108.

It will be appreciated that, where appropriate, instead of closed loopcontrol the pressure value can simply be fed through the processor toobtain a calibrated performance input value at pre-determined intervalsor otherwise. It will be further appreciated that the module 108 can beformed at various levels of sophistication, for example providingmultiple dimensional mapping tables allowing trade-offs between aplurality of desired performance output values.

A platform for an engine management system according to the presentinvention is described in more detail with reference to FIGS. 8 to 10for a system monitoring the pressures in all six cylinders of an engineand providing information concerning fuel quantity and injection, 1timing which override the corresponding outputs of a production enginecontrol unit 170.

Cylinder pressure sensors 172 are digitised by processing meanscomprising in the preferred embodiment an EMEK II intelligent dataacquisition system 174. The data acquisition system also receivessignals from sensors 176 which may include, for example, a mass air flowsensor, inlet temperature sensor, cam sensor, air/fuel ratio or lambdasensor or any other appropriate sensors of known type. As can be seenfrom FIG. 10 the data acquisition system 174 yet further receives acrank tooth signal providing a value of the crank angle (CA).

The digitised signals from the data acquisition system 174 aretransmitted to a control and diagnostics unit 178 which may comprise aC40/C167 prototyping unit developed by Hema Elektronik GmbH of Germany.The control and diagnostics unit 178 further receives data includingproduction sensor data from production engine control unit 170 and allinput data is received in external input block 180. The control anddiagnostics algorithms are configured in the preferred embodiment, inMatrixXlSystemBuild, a high level simulation and algorithm developmenttool, and downloaded as compiled code to a digital signal processing(DSP) board generally designated 182. The processed control data istransmitted from an external output block 184 of the control anddiagnostics unit 178 to the modified production engine control unit 170which controls the production actuators including, for example fuelinjectors according to their control systems and algorithms discussedabove.

It will be seen that the control and diagnostics unit 178 furtherincludes a calibration block 188 which interfaces with an externalcalibration system 190 connected, for example, to a host PC 192. Thecalibration system 190 can carry out various calibration steps. Forexample the performance input variables for obtaining a performanceoutput variable such as a desired BMEP. It will be appreciated that anyother appropriate calibration steps can equally be performed, or a modelderived equivalently.

The DSP shown generally at block 182 runs separate cylinder pressurebased EMS algorithms to implement the control strategies outlined above.

The plot in FIG. 10 is of cylinder pressure against crank angle and itwill be seen that, for each cylinder, the cycle window 200 runs over afull 7200 cycle from a crank angle significantly before TDC to a crank:angle shortly after TDC. This is followed by a data acquisition period202 allowing the finite processing time required which runs up to afirst “TN interrupt” 204. A second interrupt 206 occurs 1200 later for asix cylinder engine. Crank synchronization timing and fuel quantitycommands derived from the data acquired in the previous cycle window areapplied at the second interrupt 206 as a result of which signalprocessing 208 must take place within the interval between the first andsecond interrupts. It will be noted that as the engine speed increases,although the crank angle interval between the first and secondinterrupts remains the same, in the time domain the interval decreasesaccordingly such that the signal processing step 208 must be implementedefficiently so as not to overlap the second TN interrupt. For examplereferring to the second plot of FIG. 10, in cylinder 4, it will be seenthat the signal processing step 208 is carried out at a higher enginespeed and hence falls closer to the second IN interrupt.

The ordering of the cylinders in FIG. 11 is 1, 4, 3, 6, 2, 5.

In the preferred embodiment the timing commands generated in control anddiagnostics unit 178 are transmitted via the control area network (CAN)bus 194 to the production ECU 170 where they bypass the normal commandsgenerated by the production control algorithms. As a result the systemcan be “bolted on” in a preferred embodiment to an existing productionECU 170 with the logic appropriately modified to allow priority to themodified system in controlling production actuators.

It will be appreciated that the various embodiments discussed can becombined or interchanged and components therefrom combined orinterchanged in any appropriate manner. In particular multiple controlregimes can be combined and traded off against one another so as toachieve a compromise mode of operation meeting more than one targetoutput performance value. The approach can be applied in engine types ofdifferent configurations, stroke cycles and cylinder numbers and todifferent fuel type or combustion type internal combustion enginesincluding natural gas engines and spark or compression ignition typeengines and to different injection processes such as port-injection,direct injection, Late Compression Ignition (LCI), Homogeneous ChargeCompression Ignition (RCCI) etc. a combination of both, multi-injectionand multi-injector engines in which case the in-cylinder pressure datacan be processed generally as discussed above but modified appropriatelyto obtain data on the equivalent parameters, which data can then beapplied to appropriate actuation points dependent upon the engine type.Although the discussion above is principally applied to taking readingsand applying on a cylinder-by-cylinder and cycle-by-cycle basis.averaging techniques can be applied over multiple cylinders or cycles asappropriate.

1. A method of deriving vehicle torque comprising measuring cylinderpressure during a cylinder cycle; constructing a pressure variationfunction; obtaining work done by the engine therefrom and drivingvehicle torque from the work done.
 2. A method as claimed in claim 1further including identifying vehicle motive efficiency losses andsubtracting these from engine work done to derive vehicle torque.
 3. Amethod as claimed in claim 1 in which the vehicle motive efficiency lossis derived from a map and/or model.
 4. A method as claimed in claim 1further comprising controlling vehicle performance by adjusting aperformance input variable to control the derived vehicle torque to atarget vehicle torque.
 5. A method as claimed in claim 1 furthercomprising deriving loss from the difference between the measure ofengine shaft output and the measure of work done on a piston in thecylinder.
 6. An engine management system for an internal combustionengine having at least one cylinder pressure sensor and a data processorarranged to receive the pressure measurement during a cylinder cyclefrom the cylinder pressure sensor and process the measured pressureaccording to the method of claim
 1. 7. An engine management system foran internal combustion engine having at least one cylinder pressuresensor and at least one engine actuator and a data processor arranged toreceive pressure measurements during a cycle from the cylinder pressuresensor and an actuator controller arranged to control the actuatoraccording to a performance input variable to carry out a method asclaimed in claim
 1. 8. A computer readable medium containing processinginstructions to enable a processor to carry out a method as claimed inclaim
 1. 9. A method as claimed in claim 2 in which vehicle motiveefficiency loss is measured by skip firing an engine cylinder cycle andmeasuring corresponding vehicle deceleration.
 10. A method as claimed inclaim 3 in which the derived vehicle motive efficiency loss iscorrelated against the measured vehicle motive efficiency loss to refinethe map or model.
 11. A method as claimed in claim 5 further comprisingadjusting a performance input variable to control the measure of engineshaft output to a target value or range to obtain a target measure ofengine shaft output.
 12. A method as claimed in claim 11 furthercomprising monitoring vehicle performance by obtaining separately ameasure of engine shaft output and/or engine friction losses estimateand comparing the or each estimate against the respective derived valueto correct the estimate.
 13. A method as claimed in claim 12 furthercomprising controlling vehicle performance by adjusting a performanceinput variable to control the derived measure of engine shaft output toa target measure of engine shaft output.
 14. A method of obtaining theindicated mean effective pressure IMEP for a vehicle engine cylindercomprising measuring the cylinder pressure during a cylinder cycle,obtaining corresponding values of cylinder volume during the cycle,deriving top dead centre during the cycle, correcting the volume valuesbased on the derived value of top dead centre, and integrating pressureagainst volume to obtain the IMEP.
 15. A method as claimed in claim 14in which top dead centre is derived at a maximum pressure point of themotoring pressure curve.
 16. A method as claimed in claim 14 furthercomprising controlling vehicle performance deriving a vehicleperformance output valve from the IMEP and adjusting a vehicleperformance input variable to control the derived vehicle performanceoutput value to a target vehicle performance output value.
 17. A methodof diagnosing engine conditions in an engine with two or more cylinderscomprising the steps of skip firing individual cylinders, deriving ameasure of engine friction loss and comparing the derived loss todiagnose a respective cylinder condition.